Theses and dissertations (Engineering and Built Environment)
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Item Processing and characterization of nanoclays reinforced metal (aluminium) matrix composites(2018) Mwangi, Festus Maina; Kanny, Krishnan; Machio, Christopher N.Aluminium is currently one of the most versatile and preferred engineering material of our times. It is the world’s most abundant metal and is the third most common element on earth. The worldwide demand for aluminium has been growing steadily at an average rate of 5-7% annually. In fact, the demand has more than doubled up in the last decade. Despite the marked growth for aluminium, its alloys and composites, there is still a dire need to redesign this material’s system if it is to enjoy progressive and diverse economic feasibility and acceptability in various industrial sectors. This study opens up a new line of thought in the challenge of repositioning the material from an economic, industrial, and environmental perspective. It explores the efficacy of integrating a low-cost nanophased reinforcement system in the form of nanoclays into aluminium and/or its alloys. In the study, an experimental approach was adopted. The study called for an understanding of the intrinsic nature of both the aluminium and/or its alloys on one hand and nannoclays on the other. Based on that understanding, potential processing technologies were identified, with powder metallurgy eventually emerging as the most preferred processing route. For the current study, AMB-2712 Al alloy was used as the matrix. Two nanoclays at 1% – 12.5%wt content were experimented with as the reinforcement system, i.e. Nanofil 116 and Cloisite Ca++DEV. A conventional press and sinter approach was used to process the composites. Variables under investigation included the effects of green compaction pressure, sintering temperature profile, sintering atmosphere, and the percentage weight content of nanoclay. Besides physical inspection, hardness and tensile testing were used in comparatively evaluating the composites’ structural integrity. Thermal behaviour was assessed using DSC- TGA. Additionally, thermal conductivity, thermal diffusivity, specific heat capacity, and thermal expansion were examined with thermal-management-applications in mind. Results from the study show that nanoclays can feasibly be integrated into aluminium and/or its family of alloys and composites. Under the processing parameters used in this study, best results were obtained with 1%wt nanoclay addition. For better appreciation, both the load bearing capacity of the reference alloy and its percentage elongation to fracture were increased by more than 150%. Melting temperature was increased by 6.6%. It was also observed that the thermal conductivity, diffusivity, and specific heat capacity were not only significantly improved, but also more stable. While the results for reference sample were deteriorating after 2200C, the composites were observed to be stable at 3000C and still showing signs of potential to progress further. At 3%wt, content, the nanoclays were observed to demonstrate thermal barrier properties. Microstructural analysis portrayed the nanoclays as heat-sinks, thereby ideal for use in thermal management systems in areas such as the automotive engine components. Effects of nanoclays as revealed by microstructural analysis further demonstrated that the successful use of nanoclays as a reinforcement system for aluminium and/or its alloys presents a novel technique of preparing conventional aluminium alloys in a more economical way.Item The synthesis, structure and properties of polypropylene nanocomposites(2007) Moodley, Vishnu KribagaranPolymer nanocomposites may be defined as structures that are formed by infusing layered-silicate clay into a thermosetting orthermoplastic polymer matrix. The nanocomposites are normally particle-filled polymers for which at least one dimension of the dispersed particles is in nanoscale. These clay-polymer nanocomposites have thus attracted great interest in industry and academia due to their exhibition of remarkable enhancements in material properties when compared to the virgin polymer or conventional micro and macro-composites. The present work describes the synthesis, mechanical properties and morphology of nano-phased polypropylene structures. The structures were manufactured by melt- blending low weight percentages of montmorillonite (MMT) nanoclays (0.5, 1, 2, 3, 5 wt. %) and polypropylene (PP) thermoplastic. Both virgin and infused polypropylene structures were then subjected to quasi-static tensile tests, flexural tests, micro-hardness tests, impact testing, compression testing, fracture toughness analysis, dynamic mechanical analysis, tribological testing. Scanning electron microscopy studies were then conducted to analyse the fracture surfaces of pristine PP and PP nanocomposite. X-ray diffraction studies were performed on closite 15A clay and polypropylene composites containing 0.5, 1, 2, 3 and 5 wt. % closite 15A nanoclay to confirm the formation of nanocomposites on the addition of organo clays. Transmission electron miscopy studies were then performed on the PP nanocomposites to determine the formation of intercalated, exfoliated or agglomerated nanoclay structures. Analysis of test data show that the mechanical properties increase with an increase in nanoclay loading up to a threshold of 2 wt. %, thereafter the material properties degrade. At low weight nanoclay loadings the enhancement of properties is attributed to the lower percolation points created by the high aspect ratio nanoclays. The increase in properties may also be attributed to the formation of intercalated and exfoliated nanocomposite structures formed at these loadings of clay. At higher weight loading, degradation in mechanical properties may be attributed to the formation of agglomerated clay tactoids. Results of XRD, transmission electron microscopy studies and scanning electron microscopy studies of the fractured surface of tensile specimens verify these hypotheses.Item Fracture properties of fibre and nano reinforced composite structures(2007) Ramsaroop, AvinashInterlaminar cracking or delamination is an inherent disadvantage of composite materials. In this study the fracture properties of nano and fibre-reinforced polypropylene and epoxy composite structures are examined. These structures were subjected to various tests including Single Edge Notched Bend (SENB) and Mixed Mode Bending (MMB) tests. Polypropylene nanocomposites infused with 0.5, 1, 2, 3 and 5 weight % nanoclays showed correspondingly increasing fracture properties. The 5 weight % specimen exhibited 161 % improvement in critical stress intensity factor (KIC) over virgin polypropylene. XRD and TEM studies show an increase in the intercalated morphology and the presence of agglomerated clay sites with an increase in clay loading. The improvement in KIC values may be attributed to the change in structure. Tests on the fibre-reinforced polypropylene composites reveal that the woven fibre structure carries 100 % greater load and exhibits 275 % lower crack propagation rate than the chopped fibre specimen. Under MMB conditions, the woven fibre structure exhibited a delamination propagation rate of 1.5 mm/min which suggests delamination growth propagates slower under Mode I dominant conditions. The woven fibre / epoxy structure shows 147 % greater tensile modulus, 63 % greater critical stress intensity factor (KIC), and 184 % lower crack propagation rate than the chopped fibre-reinforced epoxy composite. MMB tests reveal that the load carrying capability of the specimens increased as the mode-mix ratio decreased, corresponding to an increase in the Mode II component. Delamination was through fibre–matrix interface with no penetration of fibre layers. A failure envelope was developed and tested and may be used to determine the critical applied load for any mode-mix ratio. The 5 weight % nanocomposite specimen exhibited a greater load carrying capability and attained a critical stress intensity factor that was 10 % less than that of the fibre-reinforced polypropylene structure, which had three times the reinforcement weight. Further, the nanocomposite exhibited superior strain energy release rates to a material with ten times the reinforcement weight. The hybrid structure exhibited 27 % increase in tensile modulus over the conventional fibre-reinforced structure. Under MMB conditions, no significant increase in load carrying capability or strain energy release rate over the conventional composite was observed. However, the hybrid structure was able to resist delamination initiation for a longer period, and it also exhibited lower delamination propagation rates.